Kenya’s electoral commission chairman has admitted its database was a target of an unsuccessful hacking attempt, but it has failed to convince the opposition, which continues to dispute the results.

Wafula Chebukati’s remarks came on Thursday following allegations by opposition leader Raila Odinga that hackers infiltrated the database and manipulated results in favour of President Uhuru Kenyatta after Tuesday’s vote.

Chebukati said “hacking was attempted but did not succeed” and tallying of final results was continuing.

With results from 97.6 percent of polling stations counted, Kenyatta held a strong lead.

Late on Thursday Odinga said most of more than 20,000 polling station result forms uploaded to the election commission’s website were fake, doubling down on previous claims of “massive” fraud in Tuesday’s presidential election.

He told Reuters news agency that most of the forms he considered fake had been filled out by agents working out of a Nairobi hotel. He provided no proof for his claim.

Earlier in the day, opposition coalition leader Musalia Mudavadi told journalists that “confidential sources” within the Independent Electoral and Boundaries Commission (IEBC) said that Odinga had won the presidential poll with 8.04 million votes against incumbent Kenyatta with 7.75 million.

A senior official in the IEBC, however, has dubbed the opposition claims as “ridiculous”. “As far as we are concerned, we don’t believe they have any credible data,” Abdi Yakub Guliye told Reuters.

Meanwhile, the electoral commission has received endorsement from the European Union. EU observers said on Thursday that they saw no signs of manipulation in the voting process, calling on whoever wins the election to try to heal political divisions in the country.

“After such competetive elections, it is now time for Kenyan politicians to bring the people together and work towards an inclusive and socially cohesive society for all Kenyans,” David McAlister, an EU observer, said at a news conference in Nairobi.

A team headed by former US Secretary of State John Kerry also called for calm and restraint on Thursday, as protests called by the opposition turned violent on Wednesday claiming the lives of at least five people.

Kerry also told Al Jazeera that the allegations need to be examined but “not a reason to stop the process or question the entire election”.

“The [counting] process is still ongoing, the counting is happening now. And as long as it’s done appropriately, you have an ability to have full integrity of this election. The integrity is still intact.”

Thabo Mbeki, the former South African president in charge of the African Union observer mission, has praised the poll so far.

“It would be very regrettable if anything emerges afterwards that sought to corrupt the outcome, to spoil that outcome,” he said.

Al Jazeera’s Catherine Soi, reporting from the opposition stronghold Kisumu, said she spoke with Odinga’s campaign team members and close advisers who still insist that the voting system was hacked.

“Raila Odinga says he needs an independent investigation into the poll and people here are saying that they have every confidence in him. They will believe everything he is going to say,” she said.

Odinga’s claims were enough to spark isolated protests in his strongholds in several Nairobi slums and the western city of Kisumu on Wednesday.

A relative peace returned to the streets on Thursday. There was violent protests in just one Nairobi neighbourhood, Kawangware slum, where police fired live rounds and tear gas as they clashed with opposition supporters.